The invention relates to casters in general, and more particularly to improvements in casters for use on heavy equipment including conveyances, machines, large aggregates and the like. More particularly, the invention relates to improvements in casters wherein a thrust bearing is interposed between the frame for the wheel or wheels of the caster and the support which is secured to or forms part of the base of a machine or the like.
It is known to interpose two ball bearings between the frame for the wheel or wheels of a heavy duty caster and the support which is mounted at the underside of the structure to be mounted on a set of casters. One ball bearing is designed to take up axial stresses and the other ball bearing takes up (primarily or exclusively) radial stresses. It is also known to use a single antifriction bearing with conical rolling elements as a substitute for a twin ball bearing; the conical rolling elements are designed to stand axial stresses but are also capable of taking up some radial stresses to ensure proper guidance of the wheel frame. A drawback of such bearings is that they require frequent adjustment as well as that their initial and installation costs are rather high. Furthermore, only a few spherical or conical antifriction rolling elements are actually called upon to take up stresses because, in most instances, the axis of the wheel is laterally offset from the vertical swivel axis of the caster. This leads to the generation of excessive localized stresses with attendant penetration of rolling elements into the adjacent races or tracks which renders it necessary to exert a substantial force in order to swivel the wheel about its vertical axis.